1989 GMC C2500 Odometer

BUFFER OUTPUT DIAGNOSIS "C" & "K" Series 1. Disconnect instrument cluster connector. Place ignition switch in the "RUN" position. Check for 12 volts between ground and Brown wire at terminal "A16". If reading is less than 12 volts, check for an open circuit in Brown wire. 2. If reading is 12 volts, check for 12 volts between ground and Brown/White wire at terminal "B17" If reading is 12 volts, replace instrument cluster. If reading is less than 12 volts, check for an open circuit in Brown/White wire. It may be necessary to enter ECM diagnostics. See COMPUTERIZED ENGINE CONTROLS section. BUFFER POWER DIAGNOSIS "C" & "K" Series 1. Disconnect instrument cluster connector. Place ignition switch in the "RUN" position. Check for 12 volts between ground and Pink/Black wire at terminal "A10". If reading is 12 volts, go to next step. If reading is less than 12 volts, check gauges fuse. Replace fuse if necessary. If fuse is okay, check for short or open in Pink/Black wire. 2. Check for 12 volts between ground and Brown/White wire at terminal "B14". If reading is 12 volts, go to next step. If reading is less than 12 volts, check speedometer fuse. Replace fuse if necessary. Check for short or open in Brown/White wire. 3. Check for 12 volts between Brown/White wire (terminal "B14") and Black/White wire (terminal "B15"). If reading is 12 volts, go to next step. If reading is less than 12 volts, check for open in Black/White wire. 4. Check for 12 volts between Brown/White wire (terminal "B14") and Black wire (terminal "B1"). If reading is 12 volts, check vehicle speed sensor circuit. See VEHICLE SPEED SENSOR TEST in this article. If reading is less than 12 volts, check for open in Black wire. NOTE: The buffer output diagnosis is to be performed only after SPEEDOMETER/ODOMETER diagnosis has been performed. NOTE: The buffer power diagnosis is to be performed only after SPEEDOMETER/ODOMETER diagnosis has been performed.